The large equilibrium discrimination for the attachment of trans-((SO3)(NH3)4Ru) to adenosine on the one hand, and a guanine derivative on the other, favoring the latter by a factor of at least 50, suggests that selective labelling of the bases in DNA will be possible. Studies with high M. W. species will be initiated and since attachment to single stranded structures may be of interest, the affinities to cytidine, uridine and thymidiene will be determined. The study with simple molecules will be extended to potential binding sites characteristic of proteins, namely - the amine groups themselves, sulfur in cysteine or methionine, and the polar groups characteristic of proline and tryptophane (studies with histidine have already been done). Work on the addition of nucleophiles to coordinated imines, particularly with nucleophiles that lead to carbon-carbon bond formation will be continued. Electronic interactions between saturated sulfur atoms located in proximity to one another will be studied, making use of the absorption in the near infra red which is characteristic of a molecule containing both Ru(II) and Ru(III), when a mechanism for electronic coupling exists. BIBLIOGRAPHIC REFERENCES: Ammineruthenium Complexes of Hydrogen Sulfide and Related Sulfur Ligands. J. Amer. Chem. Soc., 98, 689 (1976), Christa Keuhn & Henry Taube. Reduction of Pyrazine Oxide, Free and Coordinated to Ruthenium(II) Inorg. Chem., 15, 1454 (1976). M. A. Blesa and Henry Taube.